Steel and alloy structures are essential parts of civil, aviation, marine, and power generation systems. Nondestructive examination (hereinafter “NDE”) and nondestructive (hereinafter “NDT”) techniques have been an effective measure to evaluate the manufacturing quality and operational integrity of those structures and systems since the early 1970's. Many NDT and NDE techniques include ultrasonic inspection, magnetic particle inspection, electromagnetic inspection, radiographic inspection, penetrant inspection, acoustic emission and visual inspection. In particular, state-of-the-art ultrasonic NDE techniques provide an opportunity to obtain the information about internal flaws of a structure, such as voids and cracks, without damaging the structure. This information can be integrated with fracture mechanics and material properties, allowing for fatigue life prediction and risk management.
Scheduled NDEs are sometimes mandatory for structures experiencing time-dependent degradations. Inservice or field inspections are more difficult than inspections in manufacturing phases, and uncertainties in flaw identification and sizing can be much larger due to the more complex conditions for testing. The quality of NDE depends on many uncertain factors, including the sensitivity of inspection instrument, the service condition of the target structure being inspected, the variability of material properties, operation procedure and personnel and others. It would be desirable to have scientific quantification of these uncertainties in order to produce reliable and informative inspection results. Typically, deterministic treatment of the uncertainty includes the use of safety factors. However, the determination of safety factors substantially relies on experience and expert judgment, which is not a trivial task for inspection personnel such as engineers who do not have strong field knowledge.